1. Field of the Invention
The present invention relates to an ink jet recording head and an ink jet recording apparatus for discharging ink droplets from plural nozzles by driving an element substrate such as a piezoelectric element.
2. Description of the Related Art
An ink jet recording apparatus for printing on a recording medium such as paper by discharging ink droplets from plural nozzles has various advantages such as compactness, inexpensiveness and quietness, and such ink jet recording apparatuses are widely available commercially.
Such ink jet recording apparatuses utilize a piezo ink jet method whereby, for example, pressurization from a piezoelectric element causes a pressure wave to act on an ink in a pressure chamber, thereby discharging an ink droplet from a nozzle.
In response to a requirement for high-speed printing, an ink jet recording apparatus capable of printing across the entire width of a recording medium without requiring a scanning motion of an ink jet recording head has recently been proposed.
As shown in FIG. 11, an ink jet recording head 200 is provided with a head bar 202 capable of printing across the entire width of a recording medium P. In the head bar 202, head units 204 each having plural nozzles 206 are arrayed in a mutually displaced arrangement (staggered arrangement) substantially parallel to a conveyance direction of the recording medium P. Each head unit 204 has four rows of nozzles 206 in the conveyance direction of the recording medium P, in order to achieve a high resolution. The ink jet recording head 200 can print across the entire width of the recording medium P by fixedly supporting the head bar 202 and conveying the recording medium P at a predetermined pitch in a direction indicated by an arrow as shown.
Further, an ink jet recording head 210 shown in FIG. 12 is provided with a head bar 212, in which head units 214, each having plural nozzles 216 in a staggered arrangement, are arranged mutually parallel, and obliquely to a conveyance direction of a recording medium P. Each head unit 214 has two rows of nozzles 216 and is therefore of a low resolution, but a high quality image can be obtained by arranging plural head units 214 obliquely without any gaps therebetween (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 7-81049).
However, the ink jet recording head 200 shown in FIG. 11 involves wasted space because the head units 204 are arranged at a predetermined pitch in the longitudinal and transversal directions. Further, the head units 204 are increased in size in the width directions thereof (width in the conveyance direction of the recording medium P) in cases where the number of rows of the nozzles 206 is increased in order to achieve a higher resolution. Thus, the head bar 202 requires a width W at least equal to a product of the width of and the number of rows of the head units 204. As the width of the head bar 202 directly reflects on the width of the recording apparatus, the width of the head bar 202 has to be reduced in order to obtain a recording apparatus of overall compact size. Further, because printing conditions are adversely altered by the position of ink deposition in cases where the recording medium P is deformed during printing, a head bar 202 with a smaller width (namely printing area) is preferable. Further, at connecting portions of the head units 204, the nozzles used for printing an image are abruptly switched from the nozzles 206 of one head unit 204 to the nozzles 206 of another head unit 204, which is disadvantageous as this can generate streaks on printed images and because differences in characteristics between the head units 204 can become clearly evident.
In the ink jet recording head 210 shown in FIG. 12, since the head units 214 are arranged mutually parallel and in an oblique direction, a greater number of the head units 214 are required, leading to increased cost. Further, the oblique positioning of the head units 214 of rectangular shape increases a width W of the head bar 212, thus necessitating a larger size of the ink jet recording head 210. In addition, manufacture is difficult as plural head units 214 have to be precisely aligned.
On the other hand, an ink jet recording head in which head units of a trapezoidal shape, having a group of nozzles corresponding to such shape, are arrayed in an alternately inverted staggered arrangement has been proposed in order to reduce the width W of the head bar. In such an ink jet recording head, the head bar can be made with a smaller width in comparison with the ink jet recording heads 200, 210 shown in FIGS. 11 and 12, as the head units of the trapezoidal shape are arrayed in an alternately inverted staggered arrangement (see, for example JP-A No. 2003-226005, pages 5-6 and FIG. 4).
However, in this kind of ink jet recording head, in cases of irreparable nozzle clogging or damage to a discharge port, the entire head bar has to be replaced, since the head units are connected integrally. Further, since the head units have a trapezoidal shape, a wiping operation thereon in any direction geometrically causes contact with an adjacent head unit and thus maintenance cannot be carried out on the basis of individual head units.